sh-lab/tsh.c

/* 
 * tsh - A tiny shell program with job control
 * 
 * Schlittenhardt, Anna und Tran,Tuan-Dat
 */
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <ctype.h>
#include <signal.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <errno.h>

/* Misc manifest constants */
#define MAXLINE    1024   /* max line size */
#define MAXARGS     128   /* max args on a command line */
#define MAXJOBS      16   /* max jobs at any point in time */
#define MAXJID    1<<16   /* max job ID */

/* Job states */
#define UNDEF 0 /* undefined */
#define FG 1    /* running in foreground */
#define BG 2    /* running in background */
#define ST 3    /* stopped */

/* 
 * Jobs states: FG (foreground), BG (background), ST (stopped)
 * Job state transitions and enabling actions:
 *     FG -> ST  : ctrl-z
 *     ST -> FG  : fg command
 *     ST -> BG  : bg command
 *     BG -> FG  : fg command
 * At most 1 job can be in the FG state.
 */

/* Global variables */
extern char **environ;      /* defined in libc */
char prompt[] = "tsh> ";    /* command line prompt (DO NOT CHANGE) */
int verbose = 0;            /* if true, print additional output */
int nextjid = 1;            /* next job ID to allocate */
char sbuf[MAXLINE];         /* for composing sprintf messages */

struct job_t {              /* The job struct */
  pid_t pid;              /* job PID */
  int jid;                /* job ID [1, 2, ...] */
  int state;              /* UNDEF, BG, FG, or ST */
  char cmdline[MAXLINE];  /* command line */
};
struct job_t jobs[MAXJOBS]; /* The job list */
/* End global variables */


/* Function prototypes */

/* Here are the functions that you will implement */
void eval(char *cmdline);
int builtin_cmd(char **argv);
void do_bgfg(char **argv);
void waitfg(pid_t pid);

void sigchld_handler(int sig);
void sigtstp_handler(int sig);
void sigint_handler(int sig);

/* Here are helper routines that we've provided for you */
int parseline(const char *cmdline, char **argv); 
void sigquit_handler(int sig);

void clearjob(struct job_t *job);
void initjobs(struct job_t *jobs);
int maxjid(struct job_t *jobs); 
int addjob(struct job_t *jobs, pid_t pid, int state, char *cmdline);
int deletejob(struct job_t *jobs, pid_t pid); 
pid_t fgpid(struct job_t *jobs);
struct job_t *getjobpid(struct job_t *jobs, pid_t pid);
struct job_t *getjobjid(struct job_t *jobs, int jid); 
int pid2jid(pid_t pid); 
void listjobs(struct job_t *jobs);

void usage(void);
void unix_error(char *msg);
void app_error(char *msg);
typedef void handler_t(int);
handler_t *Signal(int signum, handler_t *handler);

/*
 * main - The shell's main routine 
 */
int main(int argc, char **argv) 
{
  char c;
  char cmdline[MAXLINE];
  int emit_prompt = 1; /* emit prompt (default) */

  /* Redirect stderr to stdout (so that driver will get all output
   * on the pipe connected to stdout) */
  dup2(1, 2);

  /* Parse the command line */
  while ((c = getopt(argc, argv, "hvp")) != EOF) {
    switch (c) {
    case 'h':             /* print help message */
      usage();
      break;
    case 'v':             /* emit additional diagnostic info */
      verbose = 1;
      break;
    case 'p':             /* don't print a prompt */
      emit_prompt = 0;  /* handy for automatic testing */
      break;
    default:
      usage();
    }
  }

  /* Install the signal handlers */

  /* These are the ones you will need to implement */
  Signal(SIGINT,  sigint_handler);   /* ctrl-c */
  Signal(SIGTSTP, sigtstp_handler);  /* ctrl-z */
  Signal(SIGCHLD, sigchld_handler);  /* Terminated or stopped child */

  /* This one provides a clean way to kill the shell */
  Signal(SIGQUIT, sigquit_handler); 

  /* Initialize the job list */
  initjobs(jobs);

  /* Execute the shell's read/eval loop */
  while (1) {

    /* Read command line */
    if (emit_prompt) {
      printf("%s", prompt);
      fflush(stdout);
    }
    if ((fgets(cmdline, MAXLINE, stdin) == NULL) && ferror(stdin))
      app_error("fgets error");
    if (feof(stdin)) { /* End of file (ctrl-d) */
      fflush(stdout);
      exit(0);
    }

    /* Evaluate the command line */
    eval(cmdline);
    fflush(stdout);
    fflush(stdout);
  } 

  exit(0); /* control never reaches here */
}
  
/* 
 * eval - Evaluate the command line that the user has just typed in
 * 
 * If the user has requested a built-in command (quit, jobs, bg or fg)
 * then execute it immediately. Otherwise, fork a child process and
 * run the job in the context of the child. If the job is running in
 * the foreground, wait for it to terminate and then return.  Note:
 * each child process must have a unique process group ID so that our
 * background children don't receive SIGINT (SIGTSTP) from the kernel
 * when we type ctrl-c (ctrl-z) at the keyboard.  
 */
void eval(char *cmdline) 
{
  char *argv[MAXARGS]; // Save flags for process
  int bg = parseline(cmdline, argv); // See whether cmd is back or foreground and parse cmdline
  struct job_t *job;
 
  sigset_t mask, prev_mask;
  sigfillset(&mask);
  sigprocmask(SIG_BLOCK, &mask, &prev_mask);

  if (argv[0] != NULL) { // Do nothing, but don't crash on empty line
    if (!builtin_cmd(argv)) { // if cmdline is not a builtin
     int pid = fork(); // fork process
      if (pid == 0) { // Child Process

        setpgid(getpid(), 0);
        sigprocmask(SIG_SETMASK, &prev_mask, NULL);

        if (execve(argv[0], argv, environ) != 0) { // if exec failed
          printf("%s Command not found.\n", argv[0]);
          exit(1);
        }
      } else { // Parent Process
        addjob(jobs, pid, bg ? BG : FG, cmdline);
        sigprocmask(SIG_SETMASK, &prev_mask, NULL);
        if (bg) {
          job = getjobpid(jobs, pid);
          printf("[%d] (%d) %s", job->jid, pid, cmdline);
        } else {
          waitfg(pid);
        }
      }
    }
  }
  return;
}

/* 
 * parseline - Parse the command line and build the argv array.
 * 
 * Characters enclosed in single quotes are treated as a single
 * argument.  Return true if the user has requested a BG job, false if
 * the user has requested a FG job.  
 */
int parseline(const char *cmdline, char **argv) 
{
  static char array[MAXLINE]; /* holds local copy of command line */
  char *buf = array;          /* ptr that traverses command line */
  char *delim;                /* points to first space delimiter */
  int argc;                   /* number of args */
  int bg;                     /* background job? */

  strcpy(buf, cmdline);
  buf[strlen(buf)-1] = ' ';  /* replace trailing '\n' with space */
  while (*buf && (*buf == ' ')) /* ignore leading spaces */
    buf++;

  /* Build the argv list */
  argc = 0;
  if (*buf == '\'') {
    buf++;
    delim = strchr(buf, '\'');
  }
  else {
    delim = strchr(buf, ' ');
  }

  while (delim) {
    argv[argc++] = buf;
    *delim = '\0';
    buf = delim + 1;
    while (*buf && (*buf == ' ')) /* ignore spaces */
      buf++;

    if (*buf == '\'') {
      buf++;
      delim = strchr(buf, '\'');
    }
    else {
      delim = strchr(buf, ' ');
    }
  }
  argv[argc] = NULL;
    
  if (argc == 0)  /* ignore blank line */
    return 1;

  /* should the job run in the background? */
  if ((bg = (*argv[argc-1] == '&')) != 0) {
    argv[--argc] = NULL;
  }
  return bg;
}

/* 
 * builtin_cmd - If the user has typed a built-in command then execute
 *    it immediately.  
 */
int builtin_cmd(char **argv) 
{
  if (!strcmp(argv[0], "quit")) {
    exit(0);
  } else if (!strcmp(argv[0], "jobs")) {
    listjobs(jobs);
    return 1;
  } else if (!strcmp(argv[0], "bg") || !strcmp(argv[0], "fg")) {
    do_bgfg(argv);
    return 1;
  }
  return 0;     /* not a builtin command */
}

/* 
 * do_bgfg - Execute the builtin bg and fg commands
 */
void do_bgfg(char **argv) 
{
  struct job_t *job;
  int jid;
  pid_t pid;
                
  // if arg empty
  if(argv[1]==NULL){
    fprintf(stderr,"%s command requires pid or %%jobid argument\n",argv[0]);
    return;
  } else if(argv[1][0] == '%') { // if looking for jid
    jid = atoi(&argv[1][1]);
    if(!jid){
      printf("%s: argument must be a pid or %%jobid\n", argv[0]);
      return;
    }
    job = getjobjid(jobs, jid);
    if(job == NULL) {
      printf("%s no such job\n", argv[1]);
      return;
    }
  } else { // if looking for pid
    pid = atoi(argv[1]);
    if(!pid){
      printf("%s: argument must be a pid or %%jobid\n", argv[0]);
      return;
    }
    job = getjobpid(jobs, pid);
    if(job == NULL){ 
      printf("(%s) no such process\n", argv[1]);
      return;
    }
  }

  if (job->state == ST) {
    kill(-job->pid, SIGCONT); // continue process of the job
  }

  job->state = strcmp(argv[0], "fg") == 0 ? FG : BG; // set the state to the new state

  if (job->state == FG) {
    waitfg(job->pid); // if foreground, wait for the foreground job
  } else {
    printf("[%d] (%d) %s", job->jid, job->pid, job->cmdline);
  }
  
  return;
}

/* 
 * waitfg - Block until process pid is no longer the foreground process
 */
void waitfg(pid_t pid)
{
  while (pid == fgpid(jobs)) {
    sleep(1); // busy loop
  }
  return;
}

/*****************
 * Signal handlers
 *****************/

/* 
 * sigchld_handler - The kernel sends a SIGCHLD to the shell whenever
 *     a child job terminates (becomes a zombie), or stops because it
 *     received a SIGSTOP or SIGTSTP signal. The handler reaps all
 *     available zombie children, but doesn't wait for any other
 *     currently running children to terminate.  
 */
void sigchld_handler(int sig) 
{
  int tmp_errno = errno;
  sigset_t mask, prev_mask;
  int child_status;
  pid_t wpid;
  sigfillset(&mask);

  while ((wpid = waitpid(-1, &child_status, WNOHANG | WUNTRACED)) > 1) {
    if (wpid < 0) {
      unix_error("waitpid error");
      return;
    }
    sigprocmask(SIG_BLOCK, &mask, &prev_mask);
    struct job_t *job = getjobpid(jobs, wpid);

    if (WIFSTOPPED(child_status)) {
      printf("Job [%d] (%d) stopped by signal %d\n", job->jid, jobs->pid, SIGTSTP);
      job->state = ST;
    } else if (WIFEXITED(child_status)) {
      deletejob(jobs, wpid);
    } else if (WIFSIGNALED(child_status)) {
      printf("Job [%d] (%d) terminated by signal %d\n", job->jid, jobs->pid, SIGINT);
      deletejob(jobs, wpid);
    }

    sigprocmask(SIG_SETMASK, &prev_mask, NULL);
  }

  errno = tmp_errno;
}

/* 
 * sigint_handler - The kernel sends a SIGINT to the shell whenver the
 *    user types ctrl-c at the keyboard.  Catch it and send it along
 *    to the foreground job.  
 */
void sigint_handler(int sig) 
{
  int tmp_errno = errno;
  pid_t fg_pid = fgpid(jobs);

  if (fg_pid) {
    kill(-fg_pid, SIGINT);
  }

  errno = tmp_errno;

  return;
}

/*
 * sigtstp_handler - The kernel sends a SIGTSTP to the shell whenever
 *     the user types ctrl-z at the keyboard. Catch it and suspend the
 *     foreground job by sending it a SIGTSTP.  
 */
void sigtstp_handler(int sig) 
{
  int tmp_errno = errno;
  sigset_t mask, prev_mask;

  sigfillset(&mask);
  sigprocmask(SIG_BLOCK, &mask, &prev_mask);

  pid_t fg_pid = fgpid(jobs);

  kill(-fg_pid, SIGTSTP);

  sigprocmask(SIG_SETMASK, &prev_mask, NULL);
  errno = tmp_errno;
  return;
}

/*********************
 * End signal handlers
 *********************/

/***********************************************
 * Helper routines that manipulate the job list
 **********************************************/

/* clearjob - Clear the entries in a job struct */
void clearjob(struct job_t *job) {
  job->pid = 0;
  job->jid = 0;
  job->state = UNDEF;
  job->cmdline[0] = '\0';
}

/* initjobs - Initialize the job list */
void initjobs(struct job_t *jobs) {
  int i;

  for (i = 0; i < MAXJOBS; i++)
    clearjob(&jobs[i]);
}

/* maxjid - Returns largest allocated job ID */
int maxjid(struct job_t *jobs) 
{
  int i, max=0;

  for (i = 0; i < MAXJOBS; i++)
    if (jobs[i].jid > max)
      max = jobs[i].jid;
  return max;
}

/* addjob - Add a job to the job list */
int addjob(struct job_t *jobs, pid_t pid, int state, char *cmdline) 
{
  int i;
    
  if (pid < 1)
    return 0;

  for (i = 0; i < MAXJOBS; i++) {
    if (jobs[i].pid == 0) {
      jobs[i].pid = pid;
      jobs[i].state = state;
      jobs[i].jid = nextjid++;
      if (nextjid > MAXJOBS)
        nextjid = 1;
      strcpy(jobs[i].cmdline, cmdline);
      if(verbose){
        printf("Added job [%d] %d %s\n", jobs[i].jid, jobs[i].pid, jobs[i].cmdline);
      }
      return 1;
    }
  }
  printf("Tried to create too many jobs\n");
  return 0;
}

/* deletejob - Delete a job whose PID=pid from the job list */
int deletejob(struct job_t *jobs, pid_t pid) 
{
  int i;

  if (pid < 1)
    return 0;

  for (i = 0; i < MAXJOBS; i++) {
    if (jobs[i].pid == pid) {
      clearjob(&jobs[i]);
      nextjid = maxjid(jobs)+1;
      return 1;
    }
  }
  return 0;
}

/* fgpid - Return PID of current foreground job, 0 if no such job */
pid_t fgpid(struct job_t *jobs) {
  int i;

  for (i = 0; i < MAXJOBS; i++)
    if (jobs[i].state == FG)
      return jobs[i].pid;
  return 0;
}

/* getjobpid  - Find a job (by PID) on the job list */
struct job_t *getjobpid(struct job_t *jobs, pid_t pid) {
  int i;

  if (pid < 1)
    return NULL;
  for (i = 0; i < MAXJOBS; i++)
    if (jobs[i].pid == pid)
      return &jobs[i];
  return NULL;
}

/* getjobjid  - Find a job (by JID) on the job list */
struct job_t *getjobjid(struct job_t *jobs, int jid) 
{
  int i;

  if (jid < 1)
    return NULL;
  for (i = 0; i < MAXJOBS; i++)
    if (jobs[i].jid == jid)
      return &jobs[i];
  return NULL;
}

/* pid2jid - Map process ID to job ID */
int pid2jid(pid_t pid) 
{
  int i;

  if (pid < 1)
    return 0;
  for (i = 0; i < MAXJOBS; i++)
    if (jobs[i].pid == pid) {
      return jobs[i].jid;
    }
  return 0;
}

/* listjobs - Print the job list */
void listjobs(struct job_t *jobs) 
{
  int i;
    
  for (i = 0; i < MAXJOBS; i++) {
    if (jobs[i].pid != 0) {
      printf("[%d] (%d) ", jobs[i].jid, jobs[i].pid);
      switch (jobs[i].state) {
      case BG: 
        printf("Running ");
        break;
      case FG: 
        printf("Foreground ");
        break;
      case ST: 
        printf("Stopped ");
        break;
      default:
        printf("listjobs: Internal error: job[%d].state=%d ", 
               i, jobs[i].state);
      }
      printf("%s", jobs[i].cmdline);
    }
  }
}
/******************************
 * end job list helper routines
 ******************************/


/***********************
 * Other helper routines
 ***********************/

/*
 * usage - print a help message
 */
void usage(void) 
{
  printf("Usage: shell [-hvp]\n");
  printf("   -h   print this message\n");
  printf("   -v   print additional diagnostic information\n");
  printf("   -p   do not emit a command prompt\n");
  exit(1);
}

/*
 * unix_error - unix-style error routine
 */
void unix_error(char *msg)
{
  fprintf(stdout, "%s: %s\n", msg, strerror(errno));
  exit(1);
}

/*
 * app_error - application-style error routine
 */
void app_error(char *msg)
{
  fprintf(stdout, "%s\n", msg);
  exit(1);
}

/*
 * Signal - wrapper for the sigaction function
 */
handler_t *Signal(int signum, handler_t *handler) 
{
  struct sigaction action, old_action;

  action.sa_handler = handler;  
  sigemptyset(&action.sa_mask); /* block sigs of type being handled */
  action.sa_flags = SA_RESTART; /* restart syscalls if possible */

  if (sigaction(signum, &action, &old_action) < 0)
    unix_error("Signal error");
  return (old_action.sa_handler);
}

/*
 * sigquit_handler - The driver program can gracefully terminate the
 *    child shell by sending it a SIGQUIT signal.
 */
void sigquit_handler(int sig) 
{
  printf("Terminating after receipt of SIGQUIT signal\n");
  exit(1);
}